1. Field of the Invention
The invention relates to the field of shoes. More particularly, the invention relates to shoe soles.
2. Description of the Prior Art
The natural design of the foot enables a smooth rolling motion throughout a step when walking. Studies of people's footprints in sand show that the foot rolls from heel to toe and, at the same time, also from an outside slant (supination) to an inside slant (pronation), in a smooth rolling motion. The step begins with setting the heel down on the walking surface and ends with the large toe pushing the foot off the walking surface. The toe at the end of the step and the heel at the beginning of the step are on the same plane. The center of gravity of the person is applied forward of the ankle, so that, in a normal standing position, the greatest portion of body weight is borne by the front portion of the foot, i.e., the ball and toes, and not the heel.
Traditional shoe soles cancel much of this natural design. Most traditional shoe soles are constructed with a heel portion that raises the bottom horizontal plane of the heel above the bottom horizontal plane of the ball of the foot and toes. This orientation of the foot distorts the natural interaction of certain foot joints and ligaments and results in chronic tension that leads to inflammation of various foot joints. With these traditional shoe soles, when the step begins, the heel is set down at an elevated level above the walking surface. The ball of the foot and the toes are at an unnatural angle relative to the heel, and, as the foot moves through the step, the ball of the foot drops, rather than rolls, onto the walking surface. The joints and ligaments are not in their natural and intended orientations and, as a result, the toe cannot push the foot away from the walking surface naturally. The raised heel portion forces the center of gravity of the body off-center, back toward the ankle and heel. Too much weight is placed on the heel. This overloads certain joints in the foot and causes bone spurs and other problems in the heel. The shift in the center of gravity also typically causes misalignment of the knees and of the hips. Many of the muscles intended to be used in walking are not used properly and, as a result, atrophy from lack of use. This chronic misalignment of the foot during walking leads to foot fatigue and the development of chronic postural problems, with the result that many people complain of problems with their feet, ankles, knees, and even lower spine.
Traditional shoe soles also inhibit the natural rolling motion from the outside edge to the inside edge of the foot as it goes through the step motion. Traditional shoe soles flex only along lines that run transverse to the longitudinal direction of the shoe sole, and are typically constructed to prevent flexure in the longitudinal direction, that is, they do not flex along longitudinal lines, from the outer side to the inner side of the foot.
Many efforts have been made over the years to construct a shoe sole that promotes a healthy and natural walking gait, alleviates foot pain, and does not cause fatigue. Some shoe soles have a negative heel portion. This type of sole creates tension in other parts of the foot and lower spine and does not promote a natural gait. Some shoe soles are constructed with a tripartite sole. The middle portion of the tripartite sole presents a flat bottom surface. The front portion of the sole has a flat bottom surface that is angled upward relative to the middle portion. The rear portion of the sole also has a flat bottom surface that is also angled upward, relative to the middle portion, but at a lesser angle than that of the front portion. The upper surface of the sole is flat, from heel to toe. Thus, the sole does not support the arch or the toes. The tripartite lower surface causes an abrupt rocking motion through the step and also requires that the wearer have a good sense of balance.
Conventional shoe soles have a flat upper surface. A formed insole is the placed on top of the shoe sole. This insole is typically made of a soft, cushioning material, and does not provide the even, continuous support along the bottom of the foot that is needed when walking.
What is needed, therefore, is a shoe sole that allows the foot to roll naturally from heel to toe and side to side. What is further needed is such a shoe sole that supports the entire foot throughout the entire step.